This invention relates to antenna assemblies, and more particularly to a reflector for use with an antenna disposed within a radome on a mobile platform such as an aircraft for reducing reflections of electromagnetic energy within the radome.
Antennas are now being used on the exterior surfaces of commercial aircraft to provide broadband interconnectivity with ground based stations via one or more satellite-based transponders. Such antennas are often electronically scanned phased array antennas, mechanically augmented phased array antennas, or other forms of reflector antennas which are disposed on an exterior surface of the fuselage of the aircraft. The antenna is typically mounted within a radome and radiates its beam through the radome when in a transmit mode of operation.
An undesirable consequence of mounting the phased array antenna within the radome is the creation of reflections of electromagnetic energy caused by the radiated electromagnetic energy impinging the radome at angles other than normal to the interior surface of the radome. However, when electromagnetic energy impinges the radome at an angle normal to the surface of the radome, the great majority of the energy passes through the radome. The problem with reflected energy is particularly acute when the main beam from the antenna is scanned at a scan angle of between about 30xc2x0-75xc2x0 from the boresight of the antenna, which causes the beam to be directed along an axis which is close to parallel to the exterior of the fuselage of the aircraft. At this scan angle, the electromagnetic energy impinges an interior surface of the radome which is tapering toward the fuselage. Electromagnetic energy impinges the interior surface at an angle which is not normal thereto, thus causing a significant degree of energy to be reflected by the interior surface of the radome back toward the aircraft. This situation is highly undesirable as such reflected energy can be directed into the skin of the aircraft, wherein the skin can act as an antenna to further radiate the energy towards other RF receivers or transceivers in the vicinity of the aircraft, and particularly transceivers located on the ground below the aircraft. Since the radome must have a highly aerodynamic shape, it becomes impossible to avoid the problem of reflections within the radome because at such angles as described above (i.e., about 30xc2x0-75xc2x0), the main beam radiated by the antenna will always be impinging the walls of the radome at angles that are not normal to the interior surface of the radome.
Accordingly, it would be highly desirable to provide some form of reflector within the radome which at least partially circumscribes the antenna to reflect a portion of the radiated electromagnetic energy from the antenna toward the interior surface of the radome such that the reflected electromagnetic energy impinges the interior surface of the radome at an angle normal thereto, thus minimizing the reflections that occur within the radome when the antenna is scanned to an angle greater than about 30xc2x0 off of its boresight.
It would also be highly desirable to provide such a reflector as described above that does not interfere with operation of the antenna, whether the antenna is an electronically scanned phased array antenna or a mechanically augmented phased array antenna, or other form of reflector antenna, and further which does not require modifications to the shape of the radome or necessitate non-aerodynamic modifications to the contour of the radome.
The present invention is directed to a reflector for use within a radome mounted on an exterior surface of a mobile platform. In the embodiment illustrated and described herein, the radome is adapted to be secured to an exterior surface of a commercial aircraft.
The reflector comprises a frustoconical member which is adapted to be mounted to the exterior surface of the mobile platform on which the radome is mounted. The reflector, in one preferred form, is circular and completely circumscribes the antenna. In a preferred embodiment the reflector also includes a base portion which forms a planar panel adapted to be disposed against or adjacent to the outer surface of the mobile platform on which the radome is mounted. The base portion can support the antenna directly thereon or can be used to support an intermediate component which itself is supporting the antenna. The reflector, as well as the base, is preferably manufactured from a thin metallic sheet and includes a layer of radar absorbing material (RAM) on an upper surface thereof. The reflector is formed such that it diverges from the outer surface of the mobile platform. The angle of divergence is dependent on the precise contour of the radome.
In the preferred embodiment, at least one independent reflecting plate is disposed on an exterior surface of the mobile platform outwardly of the reflector to further absorb reflected electromagnetic energy that would otherwise be directed by the interior surface of the radome back into the metallized skin of the mobile platform.
The angle of the reflector is further selected based on the contour of the radome, and further such that the reflector will intercept a portion of the main beam radiated from the antenna, when the main beam is scanned at an angle greater than about 30xc2x0 off of the boresight of the antenna, such that a portion of the radiated electromagnetic energy is reflected by the reflector plate towards the radome and impinges the radome at an angle normal to the interior surface of the radome. In this manner the great majority of the reflected electromagnetic energy from the reflector passes through the radome without the radome causing any further reflections thereof toward the mobile platform.
The reflector of the present invention can thus be used with a wide variety of antennas and does not require modifications to the aerodynamic shape of the radome, which is extremely important in maintaining a smooth aerodynamic profile for the radome.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.